Welding Aluminum - Questions and Answers - A Practical Guide for Troubleshooting Aluminum Welding-Related Problems

258 Pages·2010·6.43 MB·English

by  Anderson

Welding Aluminum—
Questions and Answers
A Practical Guide for Troubleshooting
Aluminum Welding-Related Problems
2nd Edition
by
Tony Anderson, CEng, FWeldI, CWEng
Reviewed by the
AWS Product Development Committee
This publication is designed to provide information in regard to the subject matter
covered. It is made available with the understanding that the publisher is not engaged
in the rendering of professional advice. Reliance upon the information contained in
this document should not be undertaken without an independent verification of its
application for a particular use. The publisher is not responsible for loss or damage
resulting from use of this publication. This document is not a consensus standard.
Users should refer to the applicable standards for their particular application.
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WELDING ALUMINUM—QUESTIONS AND ANSWERS
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ii
WELDING ALUMINUM—QUESTIONS AND ANSWERS
Preface
The 2nd edition of this book was produced in order to include additional sections
which contain material considered important and very appropriate for enhancing the
overall content of the publication.
The additional topics that have been added are:
1. The Reduction in Strength of Aluminum Base Material after Welding—and the
effect of filler alloy selection on the strength of fillet welds, with tables providing
valuable data.
2. Post Weld Processing—how to regain lost strength and return aluminum alloys to
their original condition after welding—considerations of both heat treatable and
non-heat treatable alloys.
3. Explanations of Aluminum Heat Treatment Terms—such as solid-solution
hardening, precipitation hardening, age hardening, natural aging, artificial aging,
annealing, stabilizing, and stress-relieving, and their affect on aluminum alloys.
4. The use of Aluminum in Cryogenic Applications—with tables that show how
mechanical properties of aluminum alloys increase as the temperature decreases.
5. Exfoliation Corrosion and Intergranular Corrosion in Aluminum—ASTM
document designation: B928/B928M Standard Specification for High Magnesium
Aluminum-Alloy Sheet and Plate for Marine Service and Similar Environments.
6. Modes of Metal Transfer Preferable to Aluminum Welding and Why—with table
showing GMAW globular-to-spray transition currents for a selection of aluminum
electrode diameters for welding aluminum with pure argon shielding gas.
7. Open Root Joint Welding of Aluminum Pipes—the difference between welding
aluminum alloys and steel using the gas tungsten arc welding process for this
specialized application.
8. Stud Welding of Aluminum—Drawn Arc Stud Welding of Aluminum and
Capacitor Discharge Stud Welding of Aluminum.
9. An Overview of Plasma Arc Cutting of Aluminum—a comparison of plasma arc
cutting, laser cutting, and water jet cutting.
10. Brazing and Soldering of Aluminum Alloys—an overview of the many brazing and
soldering techniques.
11. Welding Specification for Friction Stir Welding—an overview of the AWS D17.3/
D17.3M:2010, Specification for Friction Stir Welding of Aluminum Alloys for
Aerospace Applications.
iii
WELDING ALUMINUM—QUESTIONS AND ANSWERS
As with the 1st edition, this book is largely comprised of individual Aluminum
Questions and Answers that were originally published over a number of years in the
American Welding Society (AWS) Welding Journal. The majority of the questions
addressed herein originate from inquiries to me, primarily from individuals within
the welding fabrication industry.
Also included in this collection of material are some feature articles that I have had
published previously in the Welding Journal. The welding processes section (Chapter
7) contains information and parameters graciously provided by The Aluminum Associ-
ation and reproduced from their outstanding publication “Welding Aluminum Theory
and Practice—Fourth Edition.” Many of the graphics and charts within this book have
been reproduced with permission from ESAB Welding and Cutting Products and were
taken from material that is used by ESAB for their aluminum welding technology
training programs. This book is not constructed in the format that is typically associ-
ated with text books pertaining to similar subjects. That is to say, because of the
nature of the material source used for this book, the Aluminum Q&A columns, the
individual chapters within this book have been compiled to best highlight and explain
that material in a manner that reflects the original question and answer theme. For
this reason the book deviates from the more traditional layout of a textbook, where
typically you would see all the information on specific topics grouped together more
specifically.
The idea for compiling this book originated through inquiries from individuals who
followed the Aluminum Q&A column in the Welding Journal enthusiastically. They
wondered if anyone had ever thought of collecting all the information within the Alu-
minum Q&A columns together into a practical guide for troubleshooting aluminum
welding-related problems. I have tried to present this material in a logical format and
have included a fairly comprehensive table of contents and index in an attempt to
direct the reader to their appropriate areas of interest. If the information contained in
this publication helps individuals to better understand aluminum welding and pos-
sibly assists in improving welding quality, then I will be pleased with the overall
outcome.
Tony Anderson, CEng, FWeldI, CWEng
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WELDING ALUMINUM—QUESTIONS AND ANSWERS
Table of Contents
Section Page
Preface..............................................................................................................................iii
About the Author...............................................................................................................v
List of Questions..........................................................................................................xviii
List of Tables...................................................................................................................xx
List of Figures.................................................................................................................xxi
Basic Safety Precautions...............................................................................................xxv
Chapter 1—The Advancement of Aluminum within the Welding
Fabrication Industry and its Many Product Design Applications.....................1
1.1 Introduction..............................................................................................................1
1.2 Automotive Industry................................................................................................1
1.3 Shipbuilding..............................................................................................................3
1.4 Recreation and Sporting Equipment.......................................................................5
1.5 Transportation and Containers...............................................................................7
1.6 Defense and Aerospace.............................................................................................8
1.7 Conclusion...............................................................................................................10
Chapter 2—What is the History of Aluminum and Aluminum Welding?........11
2.1 Introduction............................................................................................................11
2.2 The Story Behind the Metal...................................................................................12
2.3 Developments in Welding Aluminum....................................................................13
2.4 The History of Heliarc Welding (Gas Tungsten Arc Welding).............................16
2.5 Gas Welding (Oxyacetylene Welding)....................................................................17
2.6 Stick Electrode Welding (Shielded Metal Arc Welding).......................................18
2.7 Conclusion...............................................................................................................18
Chapter 3—Aluminum Alloys and Metallurgy......................................................19
3.1 The Aluminum Alloy Designation System.....................................................19
3.1.1 Introduction...............................................................................................19
3.1.2 Wrought Alloy Designation System..........................................................19
3.1.3 Cast Alloy Designation..............................................................................20
3.1.4 The Aluminum Temper Designation System...........................................20
3.1.5 Aluminum Alloys and Their Characteristics...........................................23
3.1.6 1xxx Series Alloys......................................................................................23
3.1.7 2xxx Series Alloys......................................................................................23
3.1.8 3xxx Series Alloys......................................................................................24
3.1.9 4xxx Series Alloys......................................................................................24
3.1.10 5xxx Series Alloys......................................................................................24
3.1.11 6xxx Series Alloys......................................................................................25
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WELDING ALUMINUM—QUESTIONS AND ANSWERS
Section Page
3.1.12 7xxx Series Alloys.....................................................................................25
3.1.13 Conclusion.................................................................................................25
3.2 What is the Affect of Arc Welding on the Heat-Affected Zone
(HAZ) of Aluminum Alloys?..............................................................................26
3.2.1 Introduction...............................................................................................26
3.2.2 The Various Types of Aluminum Alloys..................................................26
3.2.3 The Principal Effects of Alloying Elements in Aluminum......................26
3.2.4 Pure Aluminum 1xxx................................................................................26
3.2.5 Copper (Cu) 2xxx.......................................................................................26
3.2.6 Manganese (Mn) 3xxx...............................................................................27
3.2.7 Silicon (Si) 4xxx.........................................................................................27
3.2.8 Magnesium (Mg) 5xxx...............................................................................27
3.2.9 Magnesium and Silicon (Mg Si) 6xxx......................................................27
2
3.2.10 Zinc (Zn) 7xxx............................................................................................27
3.2.11 How Aluminum Alloys Obtain Their Strength.......................................28
3.2.12 Strain Hardening......................................................................................28
3.2.13 Heat Treatment.........................................................................................28
3.2.14 The Affect of Arc Welding on the Heat-Affected Zone............................28
3.2.15 Nonheat-Treatable Alloys.........................................................................30
3.2.16 Heat-Treatable Alloys...............................................................................30
3.2.17 Conclusion.................................................................................................30
3.3 Is There a Filler Alloy that Can be Used to Weld All Aluminum
Base Alloys, and How Do I Weld Aluminum Alloys 7075 and 2024?..........31
3.3.1 A Filler Alloy for All Aluminum Base Alloys...........................................31
3.3.2 Welding 2024 and 7075.............................................................................32
3.3.3 Conclusion.................................................................................................33
3.4 What are the Differences Between the Heat-Treatable and Nonheat-
Treatable Aluminum Alloys?............................................................................33
3.4.1 Understanding the Basic Differences Between Heat-Treatable
and Nonheat-Treatable Aluminum Alloys...............................................33
3.4.2 Nonheat-Treatable Aluminum Alloys......................................................33
3.4.3 Heat-Treatable Aluminum Alloys............................................................34
3.4.4 How Does the Type of Material, Heat-Treated or Nonheat-Treated,
Affect the Completed Strength of the Weld?...........................................34
3.4.5 Conclusion.................................................................................................35
3.5 What are the Alloying Elements in Aluminum Alloys?..............................35
3.5.1 The Addition of Alloying Elements to Aluminum...................................35
3.5.2 The Principal Effects of Alloying Elements in Aluminum......................36
3.5.2.1 Copper (Cu) 2xxx........................................................................36
3.5.2.2 Manganese (Mn) 3xxx................................................................36
3.5.2.3 Silicon (Si) 4xxx..........................................................................37
3.5.2.4 Magnesium (Mg) 5xxx...............................................................37
3.5.2.5 Magnesium and Silicon (Mg Si) 6xxx.......................................37
2
3.5.2.6 Zinc (Zn) 7xxx.............................................................................37
3.5.2.7 Iron (Fe)......................................................................................38
3.5.2.8 Chromium (Cr)...........................................................................38
3.5.2.9 Nickel (Ni)..................................................................................38
3.5.2.10 Titanium (Ti)..............................................................................38
3.5.2.11 Zirconium (Zr)............................................................................38
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WELDING ALUMINUM—QUESTIONS AND ANSWERS
Section Page
3.5.2.12 Lithium (Li).................................................................................38
3.5.2.13 Lead (Pb) and Bismuth (Bi).......................................................38
3.5.3 Conclusion..................................................................................................38
3.6 What are Weldable and Unweldable Aluminum Alloys?............................39
3.6.1 The Definition of the Tern “Unweldable”.................................................39
3.6.2 Difficult-to-Weld Alloys.............................................................................40
3.6.3 Coherence Range.......................................................................................40
3.6.4 The 2xxx-Series Alloys (Al-Cu).................................................................40
3.6.5 The 7xxx-Series Alloys (Al-Zn)..................................................................41
3.6.6 Conclusion..................................................................................................41
3.7 How do I Establish the Strengths of Aluminum Alloys, Base
Material, Welds and Filler Alloys?..................................................................42
3.7.1 Aluminum Base Alloy Strength................................................................42
3.7.2 Aluminum Filler Metal Strength and As-Welded Aluminum
Joint Strength............................................................................................42
3.7.3 The AWS Filler Metal Classification System for Aluminum..................43
3.7.4 Conclusion..................................................................................................44
3.8 What is the Affect of Natural Aging on 6061 Aluminum Base Alloy?........45
3.8.1 The Heat-Treated Condition of the Base Alloy........................................45
3.8.2 The Affect of Natural Aging After Solution Heat Treatment..................45
3.8.3 The Affect of Aging on the HAZ................................................................45
3.8.4 Heat-Treatable Filler Alloy.......................................................................48
3.8.5 Conclusion..................................................................................................48
3.9 What is the Affect of Elevated Service Temperature on 6xxx Series
Aluminum Alloys?...............................................................................................48
3.9.1 What is the Reason for this Drop in Hardness and Will the
Hardness Drop Further?...........................................................................49
3.9.2 What is the Phenomenon Behind the Hardness Drop After
Heating?.....................................................................................................49
3.9.3 Will the Hardness Drop Affect Surface Roughness (Pitting, etc.)?.........50
3.9.4 Conclusion..................................................................................................50
3.10 What is Anodized Aluminum?..........................................................................51
3.10.1 What is Anodizing?....................................................................................51
3.10.2 How is it Performed?.................................................................................51
3.10.3 Different Types of Anodizing.....................................................................52
3.10.3.1 Type I—Chromic Acid Anodizing...............................................52
3.10.3.2 Type II—Sulfuric Acid Anodizing..............................................53
3.10.3.3 Type III—Hardcoat Anodizing...................................................53
3.10.4 Sealing........................................................................................................53
3.10.5 Welding on Anodized Aluminum..............................................................53
3.10.6 Anodizing Material After Welding............................................................54
3.10.7 Conclusion..................................................................................................54
3.11 Can Stress Corrosion Cracking (SCC) Affect the 5xxx Series
Aluminum Alloys?...............................................................................................54
3.11.1 What is Stress Corrosion Cracking (SCC)?..............................................54
3.11.2 The Susceptibility of the 5xxx Series Aluminum-Magnesium
Alloys to SCC.............................................................................................55
3.11.3 Is SCC a Problem when Using the 5xxx Series Aluminum Alloys?........56
3.11.4 Conclusion..................................................................................................56
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WELDING ALUMINUM—QUESTIONS AND ANSWERS
Section Page
3.12 What are the Primary Considerations When Evaluating the
Design Strength of Welded Aluminum Structures?...................................57
3.12.1 The Reduction in Strength of the Base Material After Welding............57
3.12.2 The Effect of Filler Alloy Selection on the Strength of Fillet Welds......58
3.12.3 Conclusion.................................................................................................59
3.13 What Can be Done to Restore the Lost Strength in Aluminum
Weldments After Welding?...............................................................................60
3.13.1 The Affect of Arc Welding on Material Temper.......................................60
3.13.1.1 Nonheat-Treatable Alloys..........................................................60
3.13.1.2 Heat-Treatable Alloys................................................................60
3.13.2 Options Available for Postweld Treatment.............................................62
3.13.2.1 Nonheat-Treatable Alloys..........................................................62
3.13.2.2 Heat-Treatable Alloys................................................................62
3.13.2.3 The –T6 Temper.........................................................................62
3.13.2.4 The –T4 Temper.........................................................................63
3.13.3 Conclusion.................................................................................................64
3.14 What are the Types of Heat Treatment Used on Aluminum Alloys
and How Do They Influence Manufacturing Procedures?.......................64
3.14.1 Solid-Solution Hardening.........................................................................64
3.14.2 Precipitation Hardening...........................................................................65
3.14.3 Annealing..................................................................................................65
3.14.4 Stabilizing..................................................................................................65
3.14.5 Stress-Relieving........................................................................................65
3.14.6 Refrigeration.............................................................................................66
3.14.7 The Influence of Heat Treatment on Manufacturing Procedures..........67
3.14.7.1 Welding.......................................................................................67
3.14.7.2 Forming and Machining............................................................67
3.14.8 Conclusion.................................................................................................67
3.15 Why are Aluminum Alloys Suitable for Low Temperature
Application and Why are There No Impact Toughness
Requirements for Aluminum Filler Alloys?.................................................68
3.15.1 Cryogenic Applications.............................................................................68
3.15.2 Test Data Available for Low Temperature Applications........................69
3.15.3 Conclusion.................................................................................................70
3.16 How Can I be Assured that I am Using the Correct 5xxx Series
Aluminum Alloy for Marine Applications and Thereby Prevent
Sensitization and Intergranular Corrosion?...............................................71
3.16.1 The Problem..............................................................................................71
3.16.2 The Action Taken to Prevent Reoccurrence............................................72
3.16.3 More About the B 928 Standard..............................................................72
3.16.4 Conclusion.................................................................................................73
3.17 Where Can I Find Technical Information and Training on
Aluminum Welding?...........................................................................................74
3.17.1 Useful Textbooks.......................................................................................74
3.17.2 Training Programs for Aluminum Welding.............................................75
3.17.3 Conclusion.................................................................................................76
Chapter 4—Aluminum Filler Alloys........................................................................77
4.1 Filler Alloy Selection for Aluminum Welding..............................................77
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WELDING ALUMINUM—QUESTIONS AND ANSWERS
Section Page
4.1.1 Introduction...............................................................................................77
4.1.2 Ease of Welding.........................................................................................77
4.1.3 Critical Chemistry Ranges........................................................................77
4.1.3.1 Aluminum/Silicon Alloys—4xxx Series.....................................78
4.1.3.2 Aluminum/Copper Alloys—2xxx Series.....................................78
4.1.3.3 Aluminum/Magnesium Alloys—5xxx Series.............................78
4.1.3.4 Aluminum/Magnesium/Silicon Alloys—6xxx Series.................78
4.1.4 Crack Sensitivity.......................................................................................78
4.1.4.1 Coherence Range........................................................................79
4.1.4.2 The 2xxx Series Alloys (Al-Cu)..................................................80
4.1.4.3 The 7xxx Series Alloys (Al-Zn)...................................................80
4.1.5 Groove Weld Tensile Strength..................................................................81
4.1.6 Ductility......................................................................................................82
4.1.7 Corrosion Resistance.................................................................................82
4.1.8 Service Temperature.................................................................................82
4.1.9 Postweld Heat Treatment.........................................................................82
4.1.10 Conclusion..................................................................................................83
4.2 What Filler Alloy Should be Used to Weld 6061?.........................................84
4.2.1 How to Choose the Best Filler Alloy.........................................................84
4.2.2 Making the Choice.....................................................................................85
4.2.3 Conclusion..................................................................................................86
4.3 What are the Advantages of 4047 Filler Alloy over 4043?..........................86
4.3.1 The Difference Between 4043 and 4047 Filler Alloys..............................86
4.3.2 Conclusion..................................................................................................87
4.4 What is the Correct Filler Alloy for Welding 5083 Base Alloy,
and is the Filler Alloy I am Using the Reason Why I am Failing
the Guided-Bend Tests?.....................................................................................87
4.4.1 What is the Most Appropriate Filler Alloy?.............................................87
4.4.2 Why Did the Welded Samples Fail the Guided-Bend Test?....................88
4.4.3 Reasons Why a Welded Sample May Fail the Guided-Bend Test...........88
4.4.3.1 Discontinuities in the Welded Joint..........................................88
4.4.3.2 Using an Incorrect Testing Fixture...........................................89
4.4.3.3 Improper Sample Preparation...................................................89
4.4.4 Conclusion..................................................................................................89
4.5 Should I Use 4043 or 5356 Filler Alloy?..........................................................89
4.5.1 Choosing Between 4043 and 5356............................................................89
4.5.2 Conclusion..................................................................................................90
4.6 Are the 4xxx Series Aluminum Alloys Heat-Treatable Alloys or
Nonheat-Treatable Alloys?................................................................................91
4.6.1 Postweld Heat Treatment.........................................................................91
4.6.2 Conclusion..................................................................................................92
4.7 Which Aluminum Filler Alloys are Suitable for Sustained High-
Temperature Service?........................................................................................92
4.7.1 Introduction...............................................................................................93
4.7.2 Evaluation of Most Appropriate Filler Alloy............................................93
4.7.2.1 Filler Alloy ER4643....................................................................93
4.7.2.2 Filler Alloy ER4043....................................................................93
4.7.2.3 Filler Alloy ER4047....................................................................93
4.7.2.4 Filler Alloy ER5554....................................................................93
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WELDING ALUMINUM—QUESTIONS AND ANSWERS
Section Page
4.7.3 Conclusion.................................................................................................94
4.8 Filler Alloy Selection Chart.............................................................................95
Chapter 5— Welding Discontinuities and Weld Testing.....................................99
5.1 How to Avoid Cracking in Aluminum Alloys...............................................99
5.1.1 Introduction...............................................................................................99
5.1.2 The Primary Cracking Mechanism in Aluminum Welds........................99
5.1.2.1 The 5xxx Series Alloys (Al-Mg)...............................................100
5.1.2.2 The 6xxx Series Alloys (Al-Mg-Si)...........................................101
5.1.3 Further Considerations..........................................................................103
5.1.3.1 Coherence Range......................................................................105
5.1.3.2 The 2xxx Series Alloys (Al-Cu)................................................105
5.1.3.3 The 7xxx Series Alloys (Al-Zn)................................................105
5.1.3.4 Al-Zn-Mg Alloys.......................................................................105
5.1.3.5 Al-Zn-Mg-Cu Alloys.................................................................106
5.1.4 Be Aware.................................................................................................106
5.1.5 Conclusion...............................................................................................106
5.2 Why am I Experiencing Cracking Problems in 6061 Welds when
Using Both the GMAW and GTAW Processes?...........................................107
5.2.1 Crack Sensitivity.....................................................................................107
5.2.2 Cracking in GTAW Welds and Why the Welds May be
Cracking..................................................................................................107
5.2.3 Cracking in GMAW Welds and Why the Welds May be
Cracking..................................................................................................108
5.2.4 Conclusion...............................................................................................109
5.3 Why is the Tensile Strength Too Low in my 6061 Welds?.......................109
5.3.1 Why the 6xxx Series Base Alloys Loss Strength After
Welding and How this Condition Can be Minimized............................109
5.3.2 Conclusion...............................................................................................111
5.4 How Do I Avoid Porosity Problems in Aluminum Welds?......................111
5.4.1 How Does Porosity Occur.......................................................................111
5.4.2 Shielding During the Welding Operation..............................................112
5.4.3 Hydrocarbons..........................................................................................113
5.4.4 Moisture...................................................................................................113
5.4.5 Material Preparation Concerns..............................................................114
5.4.6 Cleaning Prior to Welding......................................................................115
5.4.7 Conclusion...............................................................................................115
5.5 Why am I Having Problems Passing Guided-Bend Tests with
6061 Base Alloy and 4043 Filler Alloy?........................................................115
5.5.1 What is a Guided-Bend Test and When is it Used?..............................116
5.5.2 Bend Testing Aluminum is Different than Bend Testing Steel...........116
5.5.3 Special Bending Conditions for Aluminum Alloys................................116
5.5.4 Conclusion...............................................................................................119
Chapter 6— Equipment, Welding Processes, and Welding Procedures........121
6.1 The Repair of Aluminum Structures...........................................................121
6.1.1 Introduction.............................................................................................121
6.1.2 Identification of Alloy Type....................................................................121
6.1.3 The Repair of Some High-Performance Aluminum Alloys...................122
6.1.4 Base Material Strength Reduction After Repair Welding....................123
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